Pico- and ultraplankton Sargasso Sea communities: variability and comparative distributions of Synechococcus spp. and algae

Abstract

Ultraplankton (0.2 to 5 ~m ) provided >88% of euphotic layer chlorophyll (Chl) at 2 Sargasso Sea stations in July/August 1986. Communities were further characterized to quantify the separate abundances of phycoerythrin-fluorescing cyanobacteria Synechococcus spp. and Chl-fluorescing algae in 0.2 to 0 6, 0.6 to 1 and 1 to 5 pm size fractions. Throughout the water-column at both stations, the majority of Synechococcus cells were consistently found in the 0.6 to 1 pm fraction; the Sargasso Sea WH7803 serogroup was not a dominant component of Synechococcus populations at any depth. Highest numbers of Synechococcus cells were always in the surface isothermal layer, where they accounted for >95 % of all ultraphytoplankton cells. At the base of the euphotic layer total numbers of photoautotrophs were low, but numbers of algae increased. The varying distribution of the 2 ultraphytoplankton components with depth was also reflected in their separate contributions to Chl concentrations, and algae were the main contributors to Chl maxima at 1 to 3 % I,. Above this depth, a pigment maximum in phycoerythrin (PE) 1-' occurred at the nitracline, coincident with a peak in primary productivity. PE maxima were due to an increase in PE content of Synechococcus cells and not to an increase in their abundance. The 2 stations did however exhibit significant differences. High surface productivity at Stn 1 was supported by nanomolar changes In nitrate concentrations, which selectively and rapidly induced a Synechococcus bloom. In contrast, the water-column characteristics of Stn 2 were relatively stable, Synechococcus spp. were less abundant throughout the water-column, while algae were twice as abundant at the Chl maximum and 0.5 O/ O llght level, where most were of picoplankton size (79 to 89 % of algae were in < 1 ,um fractions). Data suggest that there is a considerable degree of variability in the abundance, composition, and productivity of stratified oceanic ultraphytoplankton communities.

Adaptation of Synechococcus in situ determined by variability in intracellular phycoerythrin-543 at a coastal station off the Southern California coast, USA

“…Indeed, such an increase in the ratio of PE:cell with depth has been observed in field populations of Synechococcus spp. in the North Atlantic (Glover et al 1988) using a non-extractive method of PE estimation.…”

Vertical and horizontal structure of the picophytoplankton community in a stratified coastal system off New Zealand

“…Cell concentrations are generally in the range of 10 5 to 10 8 I" 1 for prokaryotic forms and 10 5 to 10 7 I" 1 for eukaryotic forms (Joint 1986). Phycoerythrin-rich prokaryotic forms appear to dominate in oligotrophic oceanic regions (Murphy & Haugen 1985;Joint 1986;Glover et al 1988). In more nutrient-rich coastal waters the composition of the population is generally more variable (Glover et al 1988) with a significant contribution by eukaryotic forms (Hall & Vincent 1990).…”

“…Phycoerythrin-rich prokaryotic forms appear to dominate in oligotrophic oceanic regions (Murphy & Haugen 1985;Joint 1986;Glover et al 1988). In more nutrient-rich coastal waters the composition of the population is generally more variable (Glover et al 1988) with a significant contribution by eukaryotic forms (Hall & Vincent 1990). The picoplankton community may also be structured vertically with an increased abundance of eukaryotic forms sometimes occurring with increasing depth (e.g., Glover, Smith & Shapiro 1985;Murphy & Haugen 1985).…”

Dynamics of picocyanobacteria in the Seto Inland Sea (Japan) during summer

“…Landry et al 1984, Campbell & Carpenter 1986a, b, Iturriaga & Mitchell 1986, Iturnaga & Marra 1988, Weisse 1988, Kudoh et al 1990, Caron et al 1991, Kuosa 1991, Sherr et al 1991, Pick & Berube 1992. Furthermore, using a sensitive chemiluminescence method for NO,-analysis, Glover et al (1988a, b) found that introduction of ca 10 nM NO3-(below the detection Limit of the conventional colorimetric method) to surface waters in the stratified Sargasso Sea was followed by a Synechococcus spp.…”